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Avian clinical pathology (Proceedings)

The biochemical profile helps the veterinarian evaluate a patient's metabolic status through three specific groups of tests (metabolites, tissue enzymes and electrolytes). This paper will provide an overview of normal and abnormal analyte values within the biochemical profile and how these help the clinician rule-in or rule-out specific diseases or disease syndromes.

Serum and Plasma proteins

Total protein concentrations in birds (3.5-5.5 g/dl) are approximately half of those of mammalian species.1 Abnormal protein levels are the result of dehydration, dyscrasias (presence of abnormal proteins) or dysproteinemias (abnormal protein concentrations or abnormal proteins in the blood). Age and stage of development may also have an influence protein concentrations.2-4

Dysproteinemias

Hyperproteinemias most commonly results from dehydration, inflammatory conditions which show a reduced albumin-globulin ration (A:G ratio), hypergammaglobulinemia (chronic inflammatory conditions) and lymphoproliferative diseases (avian leukosis in chickens or myelosis in budgerigars).1,5 Hyperproteinemia with a normal A:G ration is indicative of dehydration. Estrogen may cause an increase in globulins in females that are preparing to lay.5 Chronic diseases such as psittacosis, egg yolk peritonitis, and tuberculosis may also cause an increase in protein levels.

Decreased plasma protein levels may occur in response to hemorrhage, protein losing enteropathy, nephropathy or dermatopathy, chronic hepatic disease, malabsorption or maldigestion, cachexia, malnutrition/starvation, lymphoid hypoplasia or aplasia as in psittacine circovirus infections (PBFD) and parsitism.5-7 Fibrinogen levels are not commonly performed; however, they may increase with dehydration or inflammation and may be a valuable indicator of bacterial infection and other inflammatory conditions in various species of birds (including several Amazon parrot and macaw species) as it is in mammals.6 Hypofibrinogenemia may be indicative of hepatic disorders or coagulopathies; however, the its significance has not be evaluated in psittacine species.

Plasma Protein Electrophoresis

Protein electrophoresis (PE) is considered to be the most reliable and accurate method of assessing protein concentrations in birds.8 Five major protein fractions are identified in birds including: pre-albumin, albumin, α1, α2, β1, β2 and γ-globulins.5,8 In avian species only one or two alpha fractions and a single fraction for beta and gamma proteins are typical.8

Changes and associated disease states

The following table by Werner and Reavil summarizes the changes and associated disease states one might detect by PE:9

Calcium

Plasma calcium concentrations consist of several a protein bound fraction (bound to albumin) a fraction bound to anionic compounds (citrate, bicarbonate, phosphate, or lactate) and a free (ionized portion).1,10,11

Most alterations of plasma calcium concentrations are related to nutritional disease(s). Hypercalcemia may be the result from egg production (increased carrier proteins), hypervitaminosis D (macaw species), primary hyperparathyroidism and pseudohyperparathyroidism, osteolytic tumors, dehydration, excessive supplementation and some plant toxicoses. 1,7,12,13 Artifactual increases in calcium concentrations may result from hemolysis, bacterial contamination of blood/plasma, samples1 or as a consequence of lipemia associated with ovulation or hepatic disease. Calcium levels should always be interpreted with knowledge of plasma albumin concentrations.

Hypocalcemia may arise from hypoalbuminemia, hypoparathyroidism, secondary nutritional or renal hypoparathyroidism and hypovitaminosis D. A hypocalcemic condition of African grey parrots has been frequently documented in the literature.5,12 Although the exact etiology of this condition is uncertain, dysfunctional parathyroid glands or parathyroid hormone (PTH) are suspected as possible etiologies.14